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Litre

The litre or liter (see spelling
differences) is a unit of volume. There are two official symbols: the Latin letter
L in lower (l) and
upper case (L). The litre appears in several versions of the metric
system; although not an SI unit, it is accepted for use with the
SI. The international unit of volume is the cubic
metre (m3). One litre is equal to 0.001 cubic metre and is denoted as 1
cubic decimetre (dm3).

Origin

The word "litre" is derived from an older French unit, the litron, whose name came from Greek via
Latin. The original metric system used the litre as a base unit.

Definition

A litre is defined as a special name for a cubic decimetre (1 L = 1 dm3).
Hence 1 L ≡ 0.001 m3 (exactly). So 1000 L = 1 m3

SI prefixes applied to the litre

The litre may be used with any SI
prefix. The most commonly used is the millilitre, defined as one-thousandth
of a litre (one cubic centimetre). It is a commonly used measurement,
especially in medicine and cooking. Other units may be found in the table
below, the more often used terms are in bold.

Rough conversions

A litre is the volume of a cube with sides of 10 cm, which is slightly less
than a cube of sides 4 inches (or one-third of a foot). Twenty-seven cubes
"one-third of a foot on each side" would fit in one cubic foot, which is within
5% of the actual value of exactly 28.316846592 litres.

A nice aide-memoire is: "A litre of water's a pint and three quarters".
(Imperial pints, that is)

Explanation

Litres are most commonly used for items (such as fluids and berries) which are measured by the capacity or size of their
container, whereas cubic metres (and derived units) are most commonly used for
items measured either by their dimensions or their displacements. The litre is
often also used in some calculated measurements, such as density (kg/L),
allowing an easy comparison with the density of water.

One litre of water has a mass of almost exactly one kilogram when
measured at its maximal density, which occurs at about 4 degrees celsius.
Similarly: 1 millilitre of water has about 1 g of mass; 1,000 litres of
water has
about 1,000 kg of mass. This relationship is because the gram was originally
defined as the mass of 1 mL of water. However, this definition was abandoned in
1799 because the density of water changes with temperature and, very slightly,
pressure.

Symbol

Originally, the only symbol for the litre was l (lowercase letter l),
following the SI convention that only those unit symbols that
abbreviate the name of a person start with a capital letter.

In many English-speaking countries, the most common shape of a handwritten
Arabic digit 1 is just a vertical stroke, that is it
lacks the upstroke added in many other cultures. Therefore, the digit 1 may
easily be confused with the letter l. On some typewriters, particularly older
ones, the unshifted L key had to be used to type the numeral 1. Further, even
in some computer typefaces, the two characters are barely distinguishable. This
caused some concern, especially in the medical community. As a result, L
(uppercase letter L) was adopted as an alternative symbol for litre in 1979.
The United StatesNational Institute of
Standards and Technology now recommends the use of the uppercase letter L,
a practice that is also widely followed in Canada and Australia. In
these countries, the symbol L is also used with prefixes, as in mL and µL,
instead of the traditional ml and µl used in Europe. In the UK and Ireland,
lowercase l is used with prefixes, though whole litres are often written in
full (so, "750 ml" on a wine bottle, but often "1 litre" on a juice
carton).

Prior to 1979, the symbol ℓ (script small l, U+2113), came
into common use in some countries; for example, it was recommended by South African Bureau of Standards
publication M33 and Canada in the 1970s. This symbol can still be encountered
occasionally in some English-speaking countries, and its use is ubiquitous in
Japan and South Korea. Nevertheless, it is no longer used in most countries and
no longer officially recognised by the BIPM,
the International
Organization for Standardization due to confusion and since, in any case,
it is often not available in currently-used documentation systems.

History

In 1795, the
litre was introduced in France as one of the new "Republican Measures", and defined as one
cubic decimetre.

In 1879, the
CIPM
adopted the definition of the litre, and the symbol l (lowercase letter L).

In 1901, at
the 3rd CGPM conference, the
litre was redefined as the space occupied by 1 kg of pure water at the
temperature of its maximum density (3.98 °C) under a pressure of 1 atm. This made the litre equal to about
1.000 028 dm3 (earlier reference works usually put it at 1.000 027 dm3).

In 1964, at
the 12th CGPM conference, the
original definition was reverted to, and thus the litre was once again defined
in exact relation to the metre, as another name for the cubic decimetre, that
is, exactly 1 dm3.[1]

In 1979, at
the 16th CGPM conference, the
alternative symbol L (uppercase letter L) was adopted. It also expressed a
preference that in the future only one of these two symbols should be retained,
but in 1990 said it was still too early to do so.[2]

Colloquial and practical usage

In spoken English, the abbreviation "mL" (for millilitre) is often
pronounced as "mil", which is homophonous
with the colloquial term "mil", which is intended to mean "one thousandth of a
metre". This generally does not create confusion, because the context is
usually sufficient — one being a volume, the other a linear measurement. The
colloquial use of "mil" for millimetre for an ambiguous topic as in "5 mils of
rain fell since 9am" may, however, be confusing. And in the United States a
term of the same spelling and pronunciation means a thousandth of an inch.

The abbreviation cc (for cubic centimetre, equal to a millilitre or mL)) is a
unit of the cgs system, that preceded the MKS system, that later evolved
into the SI system. The abbreviation cc is still commonly used in many
fields including (for example) sizing for motorcycle and related sports for
combustion enginedisplacement.

In European countries where the metric
system was established well before the adoption of the SI
standard, there is still carry-over of usage from the precursor cgs
and MKS systems. In the SI system, use of prefixes for multiples of
1,000 is preferred and all other multiples discouraged. However, in countries
where these other multiples were already established, their use remains common.
In particular, use of the centi (10-2), deci (10-1), deca (10+1), and hecto
(10+2) prefixes are still common. For example, in many European countries, the
hectolitre is the typical unit for production and export volumes of beverages (milk, beer, soft drinks, etc) and for measuring the
size of the catch and quotas for fishing boats; decilitres are found in
cookbooks; centilitres indicate the capacity of drinking glasses and of small
bottles. In colloquial Dutch in Belgium, a
'vijfentwintiger' and a 'drieëndertiger' (literally 'twenty-fiver' and
'thirty-threer') are the common beer glasses, the corresponding bottles mention
25 cL or 33 cL. Bottles may also be 75 cL or half size at 37.5 cL for
'artisanal' brews or 70 cL for wines or spirits. Cans come in 25 cL, 33 cL and
50 cL aka 0.5 L. Family size bottles as for soft drinks or drinking water use
the litre (0.5 L, 1 L, 1.5 L, 2 L), and so do beer barrels (50 L, or the half
sized 25 L). This unit is most common for all other household size containers
of liquids, from thermocans, by buckets, to bath tubs; as well as for fuel tanks and
consumption for heating or by vehicles.

In countries where the metric system was adopted as the official measuring
system after the SI standard was established, common usage more
closely follow contemporary SI conventions. For example, in Canada where
the metric system is now in wide-spread use, consumer beverages are labelled
almost exclusively using litres and millilitres. Hectolitres sometimes appear
in industry, but centilitres and decilitres are rarely, if ever, used. Larger
volumes are usually given in cubic metres (equivalent to 1 kL), or thousands or
millions of cubic metres. The situation is similar in Australia, although
kilolitres, megalitres and gigalitres are commonly used for measuring water
consumption, reservoir capacities and river flows.

For larger volumes of fluids, such as annual consumption of tap water, lorry
(truck) tanks, or swimming pools, the cubic
metre is the general unit, as it is for all volumes of a non-liquid nature.
There are a few exceptions in which the litre is used for rather large volumes,
such as the irregularly shaped boot of a car or the internal size of a
microwave oven.